A suspect of the August 17 Bangkok blast, who has been referred to as Yusufu Mieraili, is escorted by soldiers and prison officers as he leaves the military court in Bangkok, Thailand, November 24, 2015. Photo: Reuters/Chaiwat Subprasom

Thai police said on Thursday that suspects wanted in connection with a bomb that ripped through a Bangkok shrine, killing 20 people, have been arrested abroad and that Thailand was in the process of requesting their extradition.

More than 120 people were wounded in the August blast, the worst peacetime bombing in Thailand's history.

So far, arrest warrants have been issued for 17 people in connection with the attack. Police have said many are thought to have fled abroad.

"We have caught more people with arrest warrants out for them in connection to this case, including Thais and foreigners, but they are currently abroad and we are in the process of working with the attorney general and foreign affairs ministry to bring them to Thailand," Police Lieutenant General Srivara Rangsibrahmanakul, deputy national police chief, told reporters.

"I cannot give more details on this as it is a sensitive matter and could impact diplomatic relationships."

There has been strong criticism of the police investigation because few facts have been clearly established. Authorities were also accused of failing to seal off the crime scene properly and rapidly hosing down the pavement before forensic evidence was recovered.

It was not immediately clear if those detained would return to Thailand to appear in court.

Two suspects arrested in Thailand were indicted by a military court last month and are currently being held at a Bangkok military base. Ten charges were brought against the pair, including illegal possession of weapons, premeditated murder and murder for the bombing.

Documents sent by prosecutors to the military court say the two men are Chinese nationals from the Muslim Uighur minority.

The men will formally hear the charges against them in February.

Police have said that the blast was in retaliation for a crackdown on human smuggling gangs earlier this year. They ruled out any link to the repatriation of 109 Uighurs to China in July.

The Uighurs are a Turkic-language speaking group that calls China's western Xinjiang region home. Some Turks see themselves as sharing cultural and religious bond with their Uighur "brothers".

The Uighur issue is sensitive for the Thai government and any link between the bomb and the deportation of people at China's behest could expose it to censure that its foreign policy led to the bomb attack.